Climate and intertidal zonation drive variability in the carbon stocks of Sri Lankan mangrove forests

Sri Lanka is at the forefront of global mangrove conservation. It is the first country to officially protect all its remaining mangrove forests and has embarked on an ambitious plan to restore 10,000 ha of wetland during the United Nations Decade of Ecosystem Restoration. One incentive for this conservation effort is a recognition, based on research mostly done elsewhere, of the importance of mangroves for carbon sequestration and storage. However, a lack of data on Sri Lankan mangrove carbon pools, especially on soil organic carbon, has been recognized as a major impediment to national climate change mitigation strategies. The current work examined both above and below-ground carbon stocks of five important mangrove forests in Sri Lanka (Rekawa, Puttalam-Kalpitiya, Pambala-Chilaw, Batticaloa and Negombo) which are situated in the three major climate zones (dry, intermediate and wet) and therefore sample the main climatic drivers of spatial variability. Above-ground carbon, below-ground root carbon and soil carbon stocks of mangroves in Sri Lanka ranged from 75.5 to 189.1 Mg C ha(-1), 7.9 to 14.3 Mg C ha(-1) and 643.6 to 1253.6 Mg C ha(-1), respectively. The highest total mangrove carbon stock was recorded from the Rekawa lagoon which is in the intermediate climate zone (1455.4 Mg C ha(-1)) while the lowest was found in the Batticaloa lagoon in the dry zone (734.7 Mg C ha(-1)). Soil carbon stocks were substantially higher in the places where vegetation biomass and stand densities are high. Soil comprised 83-90% of the total mangrove carbon stocks at all sites, highlighting the large potential for release into the atmosphere as carbon dioxide if these habitats are disturbed. Overall, our study contributes important data that broadens our current understanding of how mangrove organic carbon pools vary spatially and with climatic zone.

Automated summary

Sri Lanka is at the forefront of global mangrove conservation and has embarked on restoring wetlands. Research has found a lack of data on carbon pools in Sri Lankan mangroves, with soil organic carbon being a major component. The study provides valuable insights into the spatial variation of mangrove organic carbon pools in different climatic zones.